In known types of power seat devices, the portion of the device to which is attached the seat belt is retained on the vehicle floor or a seat rail so that the load acting on the seat belt at the time of a collision is released to the vehicle floor either directly or through the seat rail. As a result, the load of the seat belt is not applied to the link portion of the vertical lifter or to the link portion of the seat belt.
Unexamined Published Japanese Patent Application No. 7-117534 discloses a power seat device in which, as illustrated in FIG. 5, a seat belt B is retained and fixed on the side of the seat cushion C. The load acting on the seat belt B at the time of a collision is transferred from a carrier K to a housing box H by way of a link plate L1 connected to the carrier K, a rod R connected to the link plate L1, a link plate L connected to the rod R, a screw S connected to the link plate L, and eventually to the housing box H.
In this known type of power seat device, because the housing box H possesses insufficient holding strength and because the housing box possesses insufficient strength itself when the housing box is made of a synthetic resin material, the housing box H becomes loose or breaks when the load acting on the seat belt B is transferred. This of course adversely affects the overall safety of the seat.